1. Field of Invention
The present invention generally relates to a method for driving an electro-optical panel, a data line driving circuit thereof, an electro-optical apparatus, and electronic equipment.
2. Description of Related Art
Generally, an image display portion of a liquid crystal display apparatus includes an element substrate, an opposing substrate, and liquid crystal enclosed in a gap defined between these substrates. A plurality of scanning lines, a plurality of data lines, transistors provided correspondingly to the intersections of the scanning lines and the data lines, and pixel electrodes are formed on the element substrate. On the other hand, a common electrode is formed on the opposing substrate. Further, thin film transistors (hereunder referred to as xe2x80x9cTFTsxe2x80x9d) are used as the transistors.
Each TFT has a gate connected to a scanning line, a source connected to a data line, and a drain connected to a pixel electrode.
Generally, a method for driving this image display portion includes simultaneously turning on a plurality of TFTs by selecting scanning lines with predetermined timing, and then applying a voltage of each of the data lines to the pixel electrodes simultaneously. In this case, voltages corresponding to image data are supplied to the data lines, respectively. The transmittance of the liquid crystal is controlled according to the voltage applied between the pixel electrode and the common electrode. This enables gray scale display according to the values of image data.
The relationship between the voltage applied to the liquid crystal and the transmittance thereof (hereunder referred to as xe2x80x9cV-T characteristicxe2x80x9d) is not a linear relation but a non-linear relation. Therefore, it is necessary to perform an operation of making the quantity of change in transmittance of the liquid crystal uniform, correspondingly to each gray scale level of image data. In the present application, this operation is referred to as a xcex3-correction.
FIG. 17 is a block diagram illustrating a data line driving circuit for driving one data line, and peripheral circuits thereof. As shown in this figure, the data line driving circuit includes a first latch circuit 921, a second latch circuit 922, and a DA converter 93. Further, a controller 6 and a xcex3-correction circuit 91 are provided at a preceding stage of this data line driving circuit.
The controller 6 generates 6-bit image data DA. The xcex3-correction circuit 91 performs xcex3-correction on the image data DA and generates 8-bit image data DB (Dxcex31, Dxcex32, . . . , Dxcex38). Incidentally, the xcex3-correction circuit 91 includes a RAM or a ROM, in which a table for performing xcex3-correction is stored. Data stored in this table is determined according to the input-output characteristic of the DA converter 93, and the transmittance-applied-voltage characteristic of the liquid crystal.
The DA converter 93 is a capacitance division DA converter using switches and capacitors. The DA converter 93 has 8 parallel-placed capacitive devices 941 to 948. If xe2x80x9cCxe2x80x9d represents the value of capacity of the capacitive device 941, then the capacitive devices 942, 943, . . . , 948 are selected so that the values of these capacitive devices are 2C, 4C, . . . , and 128C, respectively.
Further, data line capacitance 940 is parasitic on a data line 99. In FIG. 17, the value of this parasitic capacitance is indicated by Cs. A voltage Vcom at a terminal, which is at the side opposite to the data line 99, of an equivalent capacitor having capacitance equal to the data line capacitance 940 is applied to the common electrode placed on the opposing substrate.
Two reference voltages Va and Vb are supplied to the DA converter 93. One terminal of each of the capacitive devices 941 to 948 is connected to a supply terminal Ta for supplying the reference voltage Va. On the other hand, the other terminal of each of the capacitive devices 941 to 948 is connected to the supply terminal Ta through a corresponding one of reset switches 951 to 958. When the switches 951 to 958 are on, both terminals of each of the capacitive devices 941 to 948 are short-circuited, so that the charged electricity of the capacitive devices 941 to 948 is discharged therefrom. Further, a reset switch 910 is connected to between a terminal for supplying the other reference voltage Vb and the data line 99. When this switch 910 is on, the electric potential of the data line 99 is reset to a level corresponding to the voltage Vb.
Additionally, each of switches 961 to 968, which is adapted to be on or off according to the value of a corresponding one of data Dxcex31 to Dxcex38, is provided between the data line 99 and a corresponding one of the capacitive devices 941 to 948. When switches 961 to 968 are selectively turned on, the capacitive devices connected to the switches, which are turned on, are parallel-connected to one another. Thus, a voltage corresponding to image data DB is applied to the data line 99.
Meanwhile, in recent years, liquid crystal exhibiting a nearly linear V-T characteristic has been developed by improving the composition thereof. It has been known that, especially, in the case of certain TN (Twisted Nematic) liquid crystal, as shown in a graph of FIG. 18, the V-T characteristic thereof almost rectilinearly (or linearly) changes at the white side, while such a characteristic thereof curvedly (or non-linearly) changes at the black side.
When the liquid crystal whose V-T characteristic having both of a linear portion and a non-linear portion is driven, it is considered that the liquid crystal is driven by assuming that the V-T characteristic thereof linearly changes. In this case, although the xcex3-correction circuit 91 can be omitted, the gray scale level of an actually displayed image is higher than that of an original image to be displayed, because the relation between the transmittance and the applied voltage is actually a non-linear relation at the black side. Thus, this conventional liquid crystal has a drawback in that the original image cannot be displayed with proper gray scale levels at the black side. Additionally, this conventional liquid crystal has other drawbacks in that the contrast ratio of a display using this liquid crystal is decreased, and that the picture quality thereof is degraded.
Conversely, in the case of performing xcex3-correction by using the xcex3-correction circuit 91, none of such drawbacks occur, because preliminarily xcex3-corrected image data is supplied to the data line driving circuit. However, a primary part of the xcex3-correction circuit 91 includes the RAM or ROM, as described above. Moreover, peripheral circuits, such as a read circuit, are necessary. Thus, such a conventional liquid crystal display unit has a drawback in that when the xcex3-correction circuit 91 is used, the cost and power-consumption thereof are increased.
The present invention is accomplished in view of the aforementioned circumstances. Accordingly, an object of the present invention is to provide a data line driving circuit of an electro-optical panel, which has a circuit having a small occupied area and can be driven with low power consumption, and to provide a driving method therefor, and to provide an electro-optical apparatus, and to provide electronic equipment.
To achieve the foregoing object, according to an aspect of the present invention, there is provided a method for driving an electro-optical panel on the precondition that this method is used in an electro-optical panel having an electro-optical material, whose transmittance-applied-voltage characteristic has a linear portion and a non-linear portion, a plurality of scanning lines, a plurality of data lines, switching devices provided correspondingly to intersections between the scanning lines and the data lines, and pixel electrodes provided correspondingly thereto. This method includes the step of determining, according to a value of a predetermined bit of image data to be displayed, which of the linear portion and the non-linear portion of the characteristic the image data corresponds to, the step of supplying a first voltage to a parasitic capacitance of each of the data lines, the step of charging a quantity of electric charge, on which xcex3-correction is performed, into the parasitic capacitance of each of the data lines corresponding to a data value of the image data when it is determined that the image data corresponds to the non-linear portion, and the step of charging a quantity of electric charge, on which xcex3-correction is not performed, corresponding to the data value of the image data into the parasitic capacitance of each of the data lines when it is determined that the image data corresponds to the linear portion.
According to this method of the present invention, even when the transmittance-applied-voltage characteristic of the electro-optical material has the linear portion and the non-linear portion, it is determined which of the linear portion and the non-linear portion the image data to be displayed corresponds to. Further, according to a result of the decision, a predetermined quantity of charge is charged into the parasitic capacitance of the data line. Thus, the xcex3-correction can be suitably performed. Consequently, the gray scale reproducibility and the contrast ratio of a displayed image can be simultaneously enhanced.
Further, according to another aspect of the present invention, there is provided another method for driving an electro-optical panel on the precondition that this method is used in an electro-optical panel having an electro-optical material, whose transmittance-applied-voltage characteristic has a linear portion and a nonlinear portion, a plurality of scanning lines, a plurality of data lines, switching devices provided correspondingly to intersections between the scanning lines and the data lines, and pixel electrodes provided correspondingly thereto. This method includes the step of determining, according to a value of a predetermined bit of image data to be displayed, which of the linear portion and the non-linear portion of the characteristic the image data corresponds to, and the step of selecting, when it is determined that the image data corresponds to the non-linear portion, from plural inner capacitances provided correspondingly to each of bits other than the predetermined bit of the image data and weighted according to the bit value thereof, the inner capacitances corresponding to a data value represented by the other bits, and charging a quantity of electric charge corresponding to an image data value into each of the selected inner capacitances, and supplying a voltage to each of the data lines by transferring the charge between a parasitic capacitance thereof and each of the selected inner capacitances, and the step of selecting, when it is determined that the image data corresponds to the linear portion, from the plural inner capacitances, the inner capacitances corresponding to the data value represented by the other bits, and charging a quantity of electric charge corresponding to an image data value into each of the selected inner capacitances, and supplying a voltage to each of the data lines by transferring the charge between the parasitic capacitance thereof and each of all of the inner capacitances.
According to this method of the present invention, the inner capacitances can be used for both the cases that the image data to be displayed corresponds to the linear portion (in this case, the xcex3-correction is not performed on the image data), and that the image data to be displayed corresponds to the non-linear portion (in this case, the xcex3-correction is performed on the image data). Thus, an image can be displayed by using a simple circuit. Moreover, it is determined which of the linear portion and the non-linear portion the image to be displayed corresponds to. Further, according to a result of this decision, a predetermined quantity of electric charge is charged into the parasitic capacitances of the data lines. Thus, the xcex3-correction is suitably performed on the image data. Consequently, the gray scale reproducibility and the contrast ratio of a displayed image can be simultaneously enhanced.
Further, according to another aspect of the present invention, there is provided another method for driving an electro-optical panel on the precondition that this method is used in an electro-optical panel having an electro-optical material, whose transmittance-applied-voltage characteristic has a linear portion and a nonlinear portion, a plurality of scanning lines, a plurality of data lines, switching devices provided correspondingly to intersections between the scanning lines and the data lines, and pixel electrodes provided correspondingly thereto. This method includes the step of determining, according to a value of a most significant bit of image data to be displayed, which of the linear portion and the non-linear portion of the characteristic the image data corresponds to, and, the step of selecting, when it is determined that the image data corresponds to the non-linear portion, from plural inner capacitances provided correspondingly to each of low order bits other than the most significant bit of the image data and weighted according to the bit value thereof, the inner capacitances corresponding to a data value represented by the low order bits, and connecting one of terminals of each of the selected inner capacitances to each of the data lines, and supplying a first data line voltage across both terminals of each of the selected inner capacitances and to each of the data lines, and supplying a first inner capacitance voltage to the other terminal of each of the selected inner capacitances, and the step of connecting, when it is determined that the image data corresponds to the linear portion, one of terminals of each of all of the inner capacitances to each of the data lines, and supplying a second data line voltage to the one of terminals thereof and to each of the data lines, selecting from all of the inner capacitances, the inner capacitances corresponding to a data value represented by the low order bits, and supplying a second inner capacitance voltage to the other terminal of each of the selected inner capacitances.
This method of the present invention is suitable especially for the case that the transmittance-applied-voltage characteristic at one of the black side and the white side is non-linear. In the case of employing this method, it is determined according to the most significant bit of the image data whether or not the image data corresponds to the non-linear portion. Thus, the decision can be made by a simple circuit.
Furthermore, according to another aspect of the present invention, there is provided a data line driving circuit for driving data lines of an electro-optical panel on the precondition that this circuit is used in an electro-optical panel having an electro-optical material, whose transmittance-applied-voltage characteristic has a linear portion and a non-linear portion, a plurality of scanning lines, a plurality of data lines, switching devices provided correspondingly to intersections between the scanning lines and the data lines, and pixel electrodes provided correspondingly thereto. This circuit includes plural inner capacitances provided correspondingly to each of low order bits other than a most significant bit of the image data and weighted respectively corresponding to bit values thereof, a switching device provided between each of the inner capacitances and a corresponding one of the data lines and controlled in such a manner as to be on or off according to a digit corresponding to each of bits of the image data, a first voltage supply that selects one of a first data line voltage and a second data line voltage according to the most significant bit of the image data and for supplying the selected voltage to one of terminals of each of all of the inner capacitances and to the other terminal of each of the inner capacitances to be connected thereto through the data lines and the switching device, and a second voltage supply that selects one of a first inner capacitance voltage and a second inner capacitance voltage according to the most significant bit of the image data and for supplying the selected voltage to one of terminals of each of the inner capacitances selected according to each of digits of the low order bits.
Generally, when the integration of a circuit is performed, capacitive devices occupy a relatively large area. However, according to this invention, the capacitive devices can be used for both the cases that the xcex3-correction is performed on the image data, and that the xcex3-correction is not performed thereon. Consequently, the size of the circuit can be reduced.
In the case of an embodiment of this circuit, preferably, the switching device determines, according to a digit of the most significant bit of the image data, which of the linear portion and the non-linear portion of the characteristic of the electro-optical material the image data to be displayed corresponds to. Further, when the switching device determines that the image data corresponds to the linear portion, the switching device connects one of terminals of each of the inner capacitances to each of the data lines. Moreover, conversely, when the switching device determines that the image data corresponds to the non-linear portion, the switching device selects the inner capacitance corresponding to each of digits of the low order bits and for connecting one of terminals of the selected inner capacitances to each of the data lines. According to this embodiment, even when the transmittance characteristic of the electro-optical material has the linear portion and the non-linear portion, voltage respectively corresponding to these portions can be applied to the data lines. Thus, the gray scale reproducibility and the contrast ratio of a displayed image can be simultaneously and favorably maintained. Consequently, the picture quality thereof can be considerably enhanced.
Furthermore, in the case of an embodiment of this circuit, preferably, the switching device includes plural OR-circuits each for calculating the logical OR of the most significant bit and a corresponding one of the low order bits, and switch circuits each of which is controlled by a corresponding one of the OR circuits in such a manner as to be on or off, and provided between a corresponding one of the inner capacitances and each of the data lines. According to this embodiment, the use of several gates enables the circuit to change the condition thereof between a condition, in which the xcex3-correction is performed, and another condition, in which the xcex3-correction is not performed.
Further, according to another aspect of the present invention, there is provided a data line driving circuit for driving data lines of an electro-optical panel on the precondition that this circuit is used in an electro-optical panel having an electro-optical material, whose transmittance-applied-voltage characteristic has a linear portion and a non-linear portion, a plurality of scanning lines, a plurality of data lines, switching devices provided correspondingly to intersections between the scanning lines and the data lines, and pixel electrodes provided correspondingly thereto. This circuit includes a shift register that sequentially shifts transfer pulses in every horizontal scanning period and sequentially outputs selection signals, a first latch portion that latches image data according to each of the selection signals and outputs plural dot-sequence image data, a second latch portion that latches each of dot-sequence image data in every horizontal scanning period and outputs plural line-sequence image data, and a DA conversion portion that DA-converts the line-sequence image data. In this circuit, preferably, the DA converting portion includes plural inner capacitances provided correspondingly to each of low order bits other than the most significant bit of the line-sequence image data and weighted respectively corresponding to bit values thereof, a switching device provided between each of the inner capacitances and a corresponding one of the data lines and controlled in such a manner as to be on or off according to a digit corresponding to each of bits of the line-sequence image data, a first voltage supply that selects one of a first data line voltage and a second data line voltage according to the most significant bit of the line-sequence image data and supplies the selected voltage to one of terminals of each of all of the inner capacitances and to the other terminal of each of the inner capacitances to be connected thereto through the data lines and the switching device, and a second voltage supply device that selects one of a first inner capacitance voltage and a second inner capacitance voltage according to the most significant bit of the line-sequence image data and supplies the selected voltage to one of terminals of each of the inner capacitances selected according to each of digits of the low order bits.
Moreover, according to another aspect of the present invention, there is provided an electro-optical apparatus that includes an electro-optical panel having an electro-optical material, whose transmittance-applied-voltage characteristic has a linear portion and a non-linear portion, a plurality of scanning lines, a plurality of data lines, switching devices provided correspondingly to intersections between the scanning lines and the data lines, and pixel electrodes provided correspondingly thereto, the herein-above-mentioned data line driving circuit, and a scanning line driving circuit adapted to sequentially generate scanning line signals for selecting the scanning lines and to output the generated scanning line signal to each of the scanning lines.
According to this apparatus, there is no particular necessity for providing the xcex3-correction circuit, Thus, the size of the entire circuit of the apparatus can be reduced. Additionally, this reduction in size results in decrease in the power consumption thereof.
Furthermore, according to another aspect of the present invention, there is provided electronic equipment that includes the aforementioned electro-optical apparatus of the present invention as a display portion. Thus, the present invention can provide electronic equipment with a lower-power-consumption compact display unit. Incidentally, such electronic equipment can be, for example, an engineering workstation, a pager, a hand portable telephone set, a television set, a view-finder or monitor direct view camcorder, or a car navigation system.